Conventionally, when transferring a wafer, the center position and the angle of the wafer are calculated in order to accurately set the position and the angle of the wafer. See JP 2001-230303A, for example. Furthermore, when calculating the position and the angle of that wafer, a marker such as an orientation flat or a notch provided on the circumferential edge of the wafer is often used. After the position and the angle of the wafer are calculated, an alignment apparatus accordingly adjusts the position and the angle of the wafer, so that a transfer robot can retrieve the wafer at a predetermined position and a predetermined angle.
FIGS. 8A to 8E are views showing an exemplary conventional alignment method. In this alignment method, an alignment apparatus performs alignment by rotating a wafer 8 and moving the wafer 8 in the upper-lower direction of the drawings, which corresponds to the approach direction of a transfer robot 3. Furthermore, in FIGS. 8A and 8B, each of circles indicated by the broken lines shows the predetermined position of the wafer 8 that the transfer robot 3 approaches. Hereinafter, that position may be referred to as a “regular position”. It is assumed that the center of the circle indicated by the broken line is a rotational center of the wafer 8 on the alignment apparatus. Furthermore, the predetermined angle of the wafer 8 that the transfer robot 3 approaches may be referred to as a “regular angle”. That is to say, when the transfer robot 3 retrieves the wafer 8, that wafer 8 has to be placed at the regular position and the regular angle on the alignment apparatus.
FIG. 8A is a view showing an initial position of the wafer 8 placed on the alignment apparatus. At that initial position, for example, the method of JP 2001-230303A or the like is used to calculate the center position and the angle of the wafer 8. Then, as shown in FIG. 8B, the alignment apparatus rotates the wafer 8 using the center position and the like of the wafer 8, thereby eliminating a displacement between the current position and the regular position of the wafer 8 in a direction that is orthogonal to the movement direction of the wafer 8. Next, as shown in FIG. 8C, the alignment apparatus moves the wafer 8 in the movement direction, thereby setting the wafer 8 at the regular position. Furthermore, as shown in FIG. 8D, the alignment apparatus rotates the wafer 8, thereby setting the wafer 8 at the regular angle. Subsequently, as shown in FIG. 8E, the transfer robot 3 extends its arm by a predetermined length, thereby approaching the wafer 8 that has been set at the regular position and the regular angle. As a result, the transfer robot 3 can retrieve the wafer 8 at the predetermined position and the predetermined angle.
However, according to the conventional alignment method, the alignment apparatus performs operations multiple times, i.e., rotating, moving, and further rotating the wafer 8, and, thus, this method is problematic in that the time necessary for the alignment is long.
The present invention was arrived at in order to solve the above-described problem, and it is an aspect thereof to provide an apparatus and the like capable of shortening the time necessary for the alignment.